1. Field of the Invention
The present invention relates to a large size image display device including, for example, a large number of liquid crystal display (LCD) panels, plasma display panels (PDP), or electroluminescent (EL) display panels, arranged therein. More particularly, it relates to an image display element forming the device and a manufacturing method thereof.
2. Background Art
For a large size image display device (which is also referred to as a large size display), in order to implement high performances at a low cost, there has been adopted the system in which a plurality of flat panel displays (e.g., LCD panels, PDPs, or EL display panels) as image display elements (or, display units) are arranged in a matrix.
One example of a conventional image display element forming such a large size display is shown in FIGS. 11A and 11B.
FIGS. 11A and 11B are views showing a part of the array (2-sheet array) of the image display elements. FIG. 11A is a front view, and FIG. 11B is a side view.
An image display element 30 has a front panel 31 and a back panel 32 formed of glass or the like. The front panel 31 and the back panel 32 are opposed each other with a prescribed distance therebetween, between which a plurality of pixels 33, and a plurality of electrodes (not shown) for controlling them are arranged to form a light emitting layer (or a liquid crystal layer). Thus, the periphery thereof is sealed with a seal part 34 with a seal width g1.
When a lead line for applying a voltage to the electrode is led out from the periphery of the image display element 30, namely, a joint part 35 of the adjacent image display elements 30, the lead-out margin is necessary. When a spacing Ga between the pixels 33 of the adjacent image display elements 30 at the joint part 35 is larger than a spacing Gb between pixels in the same image display element, the joint part 35 becomes noticeable.
Thus, as shown in an enlarged view of FIG. 11B, the back panel 32 is divided into two parts, and a gap part 36 is provided at the central part. A terminal 37 corresponding to the electrode is included at the gap part (which is also simply referred to as a gap) 36. An electrode pin or a lead line 38 as shown is connected to the terminal 37, to be led outside the back panel (see, e.g., JP-A-2001-251571).
With the conventional image display element shown in JP-A-2001-251571, the lead line 38 of the electrode is led out from the gap part 36 formed in the back panel 32. Therefore, this configuration is effective as the structure for making the joint parts 35 of the image display elements 30 less noticeable. However, it is configured such that the lead lines 38 are connected to a large number of terminals 37 present in the narrow gap part 36, thereby to be connected to a wiring layer. For this reason, connection with the terminals 37 becomes complicated, and further, unfavorably, the lead-out method is complicated, and the workability is bad.
A conventional image display element shown in JP-A-2008-191502 is provided in order to solve such a problem.
FIG. 12 is a perspective view showing a configuration of the image display element shown in JP-A-2008-191502. FIG. 13 is an enlarged view of an essential part of FIG. 12.
Below, the conventional image display element shown in JP-A-2008-191502 will be described.
A large number of the image display elements are arranged in a matrix to form a large screen flat panel display.
Examples of the display device of the image display element include a LCD panel, a PDP, and an EL display panel. Incidentally, the figure shows the image display element as seen from the back thereof.
As shown in FIG. 12, the image display element includes a front panel 21 formed of a glass plate or the like, a back panel 22 similarly formed of a glass plate or the like, and opposed to the front panel 21, a plurality of pixels (not shown) arranged in a matrix between both the panels, and to be selected to be in a display or non-display state, and a plurality of electrodes (not shown) for controlling the pixels. Both the panels 21 and 22 are bonded with each other with the pixels and the electrodes interposed therebetween.
The back panel 22 is divided between two adjacent pixel lines, and a gap 23 is formed at the divided portion. In the figure, the gap 23 is shown on an enlarged scale for easy understanding, but an actual gap 23 is a minute gap with, for example, a width of about 0.30 mm.
Further, the pixels are arranged in a matrix. Thus, when a reference is made to “between pixels”, there are “between transverse pixel rows” and “between longitudinal pixel columns”. However, both inclusive are referred to as “between two adjacent pixel lines”.
Incidentally, as the back panel 22, the one divided into two parts at the central part is shown. However, the number of divisions and the position for division are not limited thereto. The back panel 22 may be divided into three or more parts, and the position for division may also be another position so long as it is between adjacent pixels.
On the front panel 21 side situated at the gap 23, a plurality of electrode terminals 24 connected to the electrodes are disposed. The electrode terminals 24 are formed of, for example, the same material as that for the electrodes simultaneously, and are exposed from the gap.
On the other hand, on a back surface 22a of the back panel 22 (the back side of the opposing surface from the front panel is referred to as “back surface”), and on an end face 22b which is the end part of the gap 23, metal film wires 25 are formed.
The metal film wires 25 are formed by, for example, thick film printing. To the end parts of the metal film wires 25 on the back surface 22a side, a connector 26 is connected. The metal film wires 25 are connected to an external driving circuit via the connector 26.
The details of the wiring part are shown in FIG. 13. As shown in the figure, the wiring part is formed by aligning the electrode terminals 24 and the metal film wires 25 such that the metal film wires 25 on the end part 22b of the back panel 22 are in vertical contact with the electrode terminals 24 on the front panel 21 side with the back panel 22 bonded on the front panel 21. Then, solder 27 is coated on the contact portion with the both panels 21 and 22 being bonded together. Both the panels are locally heated to melt the solder for bonding.
Whereas, FIG. 14 is a perspective view showing the electrode connection part when the electrode terminals 24 have been led out from the peripheral end part of the front panel 21.
The following configuration is shown. The back panel 22 is configured to be slightly smaller than the front panel 21. Thus, upon superposition of both the panels, a step part 21a is formed at the end part, so that the electrode terminals 24 are exposed at the step part 21a. Thus, the electrode terminals 24 and the metal film wires 25 formed at the end part 22b of the back panel 22 come in contact with each other, and are bonded by soldering.
As described up to this point, the image display element shown in JP-A-2008-191502 includes: the front panel 21; the back panel 22 opposite to the front panel 21; a plurality of pixels (not shown) arranged in a matrix between both the panels, and to be selected to be in a display or non-display state; and a plurality of electrodes for controlling the pixels, wherein both the panels are bonded together with the pixels and the electrodes interposed therebetween. In such an image display element, the metal film wires 25 are formed on the back surface and the end face (surface of the end part 22b) of the back panel 22. The electrode terminals 24 corresponding to the metal film wires 25 formed on the end face of the back panel 22, and connected to the electrodes are disposed on the front panel 21 side. Thus, the metal film wires 25 formed on the end face 22b and the electrode terminals 24 are bonded together by soldering.
Therefore, as compared with the image display element shown in JP-A-2001-251571, leading out of electrodes is possible with a simple method from a narrow space without using an electrode lead line. This cancels the expansion of the joint width between the image display elements. When the image display elements are arrayed to form a large screen, the image quality is improved by joint shrinkage. Further, leading out of electrode lines is simplified, resulting in a reduction of the cost.
With the conventional image display element shown in JP-A-2008-191502, as shown in FIG. 12, the electrode terminals 24 and the metal film wires 25 are connected by direct soldering. This enables the electrodes to be led out from the gap (gap/groove part) 23 formed in the back panel 22.
However, this configuration is effective as the structure for making the joint parts of the image display elements less noticeable, but, at the groove part (gap part) in the vicinity of the terminal part occurring according to the thickness of the back panel 22, the processing tools (tools for soldering such as heads and needles) are still less likely to reach the soldering part (i.e., the contact part between the electrode terminal 24 and the metal film wire 25) situated at the recesses of the gap (groove part/gap) 23.
Particularly, a display device decreases in pixel pitch with an increase in resolution. Thus, it is also necessary to narrow the width of the gap part for carrying out lead-out of electrodes according to the decrease in pixel pitch. Accordingly, electrode lead-out processing becomes further difficult.
Therefore, the connection reliability between the electrode terminals 24 and the metal film wires 25 by soldering becomes a problem.
Further, solder 27 for connecting the electrode terminals 24 and the metal film wires 25 is disposed with a fine interval. For this reason, migration tends to occur, which leads to a problem in the insulation property of the electrode lead-out part.
Further, with the conventional image display element shown in FIG. 14, it is possible to lead out electrodes from the peripheral end part of the panel with ease. However, a problem is encountered in the panel shape in the vicinity of the terminal part for disposing the electrode lead line thereon, so that lead-out processing of electrodes becomes difficult.
Examples of the processing method include soldering, wire bonding, and connection by a conductive paste (e.g., Ag paste) or the like. However, at the step part in the vicinity of the terminal part occurring according to the thickness of the back panel 22, processing tools (such as a head) become less likely to reach the connection part situated at the recesses of the step part.
Incidentally, when a conductive paste is used for connection between the electrode terminals 24 and the metal film wires 25, upon shrinkage of the contact area between the conductive paste and the electrode terminal 24 with an increase in resolution of the display element, the electric connection resistance increases, or the resistance value becomes unstable by changes with time.
When the surface material of the electrode terminal 24 is Al or Cr, an oxide layer is formed on the surface, so that a favorable electric connection cannot be obtained.
Some materials of the electrode terminal 24 have a high electric connection resistance with the connection material 27 (solder or wire bonding), or largely change with time in electric contact resistance.
Further, on the surface of the electric terminal 24, a film may be formed, or the surface may be contaminated during the manufacturing step or the like. Thus, in some cases, the film or the contamination layer inhibits the electric contact between the electrode terminals 24 and the connection material 27, so that stable electric connection or a sufficiently low resistance electric connection cannot be obtained.